The emergency department (ED), sometimes termed the emergency room (ER), emergency ward (EW), accident & emergency (A&E) department or casualty department is a hospital or primary care department that provides initial treatment to patients with a broad spectrum of illnesses and injuries, some of which may be life-threatening and requiring immediate attention. Emergency departments developed during the 20th century in response to an increased need for rapid assessment and management of critical illnesses. In some countries, emergency departments have become important entry points for those without other means of access to medical care.

Upon arrival in the ED, people typically undergo a brief triage, or sorting, interview to help determine the nature and severity of their illness. Individuals with serious illnesses are then seen by a physician more rapidly than those with less severe symptoms or injuries. After initial assessment and treatment, patients are either admitted to the hospital, stabilized and transferred to another hospital for various reasons, or discharged. The staff in emergency departments not only includes doctors and nurses with specialized training in emergency medicine but in house emergency medical technicians, radiology technicians, physician assistants, volunteers, and other support staff who all work as a team to treat emergency patients and provide support to anxious family members. The emergency departments of most hospitals operate around the clock, although staffing levels are usually much lower at night. Since a diagnosis must be made by an attending physician, the patient is initially assigned a chief complaint rather than a diagnosis. This is usually a symptom: headache, nausea, loss of consciousness. The chief complaint remains a primary fact until the attending physician makes a diagnosis.

A typical emergency department has several different areas, each specialized for patients with particular severities or types of illness.

In the triage area, patients are seen by a triage nurse who completes a preliminary evaluation, before transferring care to another area of the ED or a different department in the hospital. Patients with life or limb-threatening conditions may bypass triage and to be seen directly by a physician.

The majors, or general medical, area is for stable patients who still need to be confined to bed (note that a "bed" in the ED context is almost always a gurney rather than a full hospital bed). This area is often very busy, filled with many patients with a wide range of medical and surgical problems. Many will require further investigation and possible admission. Patients who are not in need of immediate treatment are sent to the minors area. Such patients may still have been found to have significant problems, including fractures, dislocations, and lacerations requiring suturing.

A pediatric area for the treatment of children has recently become standard, to dedicate separate waiting areas and facilities for children. Some departments employ a play therapist whose job is to put children at ease to reduce the anxiety caused by visiting the emergency department, as well as provide distraction therapy for simple procedures.

Very few EDs have a dedicated area for obstetrics nowadays. In most cases, a pregnant woman who presents to the ED is sent immediately to the obstetrics ward or the Labor and Delivery unit, unless she has another medical condition that requires treatment first.

Many hospitals have a separate area for evaluation of psychiatric problems. These are often staffed by psychiatrists and psychiatry-trained nurses and psychiatric social workers. There is typically at least one room for people who are actively a risk to themselves or others (e.g. suicidal).

Emergency departments may also have a separately streamed service for minor and rapidly treatable conditions, such as minor injuries. The fast track may be staffed by emergency nurse practitioners and/or physicians, and special consultation rooms are specifically designated for this purpose. This system allows for quicker treatment of patients who may otherwise be forced to wait for more pressing cases to resolve. This part of the department may be called by several names e.g. Urgent Care Centre, Fast Track Unit or Primary Care Suite depending on the local emphasis. Where this type of service is provided on a separate site from the local ED it is called a Minor Injuries Unit or an Urgent Care Clinic.

A hospital with an emergency department usually has prominent signage reading Emergency or Accident and Emergency (often in white text on a red background) and an arrow to indicate where patients should proceed. Some American states closely regulate the design and content of such signs, and require wording such as "Comprehensive Emergency Medical Service" and "Physician On Duty"[1], to prevent persons in need of critical care from presenting to facilities that are not fully equipped and staffed.

In Malaysia the patients are triaged -one, two, three and four according to the patient's status and then seen according to the triage.(HUKM).Emergency Medicine is quite well developed in Kuala Lumpur, post graduate studies are available in various medical schools.

In the United States an emergency department is often referred to by laypeople as an emergency room (ER). Medical professionals typically call it whatever its name is within their specific hospitals, or simply "Emergency." The term "emergency room" is a misnomer, as a modern hospital's emergency facilities consist of dozens of rooms. The ED interacts with every other department in the hospital and often represents a significant percentage of the hospital's work load and finances. It is common for emergency department doctors to work for a company hired by the hospital to provide emergency services.

During the 1990s, an effort was made to change to the more accurate term emergency department (ED), which is a term increasingly used by members of the specialty internationally. The effort failed and ED never caught on among the U.S. public, perhaps because of the popularity of the TV show ER, and the heavy marketing of the euphemism "ED" for erectile dysfunction by pharmaceutical companies. However, the term does have some circulation among emergency medicine physicians. Individual hospitals may also refer to the department by different names, such as emergency ward, emergency center, emergency unit, etc.

A smaller facility that may provide assistance in medical emergencies is known as a clinic. Larger communities often provide a drop-in clinic where people with medical problems that would not be considered serious enough to warrant an emergency department visit can be seen. These clinics often do not operate on a 24 hour basis, and visiting them is sometimes less expensive than going to the ED.

In 1986 congress passed a law commonly referred to as EMTALA (Federal Emergency Medical Treatment and Active Labor Act, also known as the Patient Anti-Dumping Law) to address a growing concern that EDs were refusing to treat patients based on their ability to pay. This law requires every ED to provide a minimal level of care to all comers regardless of their ability to pay.

The EMTALA act was passed by congress in 1986. Under this law, any person presenting to an Emergency Department is entitled by law to a Medical Screening Exam. The purpose of that exam is to determine if any illness or injury is present that without immediate intervention, could have serious consequences if treatment is delayed more than 24 hours. In practice, doing so often requires a full evaluation of all patients presenting to an Emergency Department. Only after that exam is fully complete may patients be referred to an outpatient clinic or their primary care physician if their condition and/or diagnosis allows it. According to a May 2003 American Medical Association (AMA) study, emergency physicians annually provide, on average, $138,300 of uncompensated care under the aegis of EMTALA. The cost of performing these exams has resulted in growing financial losses for hospitals. Many have responded by closing their Emergency Departments, further overcrowding surrounding Emergency Departments that have stayed open. The combination of these factors has resulted in increasingly longer waits for even seriously ill patients as most EDs in America routinely operate well beyond their designed capacity. The overcrowding is further exacerbated by uninsured or under-insured patients who are forced to use Emergency Departments as their primary care facility because they have been turned away elsewhere. EDs have also been inundated with patients seeking test and/or exams that generally require long waits for approval by their HMO health plans and patients referred to the ED for admission by their primary physicians who are afraid of being denied payment for pre-admission tests a health plan administrator may decide was not medically necessary. Wait times exceeding 12 or even 24 hours are no longer uncommon in most American cities under normal circumstances. Natural or man-made disasters can now quickly overwhelm and shut down even the largest medical centers leaving people without access to any medical care. The latest example of this happening was in New Orleans after hurricane Katrina overwhelmed the cities levee system.

Most teaching hospitals and district general hospitals (DGHs) have emergency departments. The largest such department in the UK is in St Thomas' Hospital. Traditionally, waits for assessment in the A&E were very long in some areas of the UK. In October 2002, the Department of Health introduced a policy that forced departments to assess and treat patients within four hours of arrival, with referral and assessment by other departments if deemed necessary.[1]. Present policy is that 98% of all patients do not "breach" this four-hour wait.

In other countries without this policy (such as Ireland and Australia), patients may be faced with prolonged waits of hours or even days on trolleys for hospital beds.

Patients arrive at emergency departments in two main ways: by ambulance or independently. The ambulance crew notifies the hospital beforehand if they are transporting a severely-ill patient, and if the patient's condition warrants, a physician may direct the ambulance crew to begin treatment while still en route. These patients are rushed to the emergency department's resuscitation area, where they are met by a team with the expertise to deal with the patients' conditions. For example, patients with major trauma are seen by a trauma team consisting of emergency physicians and nurses, a surgeon, and an anesthesiologist (anaesthetist).

Patients arriving independently or by ambulance are typically triaged by a nurse with training in emergency medicine. Patients are seen in order of medical urgency, not in order of arrival. Patients are triaged to the resuscitation area, majors area, or minors area. Emergency/Accident and Emergency departments usually have one entrance with a lobby and a waiting room for patients with less-urgent conditions, and another entrance reserved for ambulances.

Cardiac arrest may occur in the ED/A&E or a patient may be transported by ambulance to the emergency department already in this state. Treatment is basic and advanced life support as taught in the Advanced Life Support and Advanced Cardiac Life Support courses. This is an immediately life-threatening condition which requires immediate action in salvageable cases.

An ECG that reveals ST segment elevation or new left bundle branch block suggests complete blockage of one of the main coronary arteries. These patients require immediate reperfusion (re-opening) of the occluded vessel. This can be achieved in two ways: thrombolysis (clot-busting medication) or percutaneous transluminal coronary angioplasty (PTCA). Both of these are effective in reducing significantly the mortality of myocardial infarction. Many centers are now moving to the use of PTCA as it is somewhat more effective than thrombolysis if it can be administered early. This may involve transfer to a nearby facility with facilities for angioplasty.

The services that are provided in an emergency department can range from simple x-rays and the setting of broken bones to those of a full-scale trauma center. Emergency medical technicians often work as support staff in emergency departments under the supervision of nurses and doctors. A patient's chances of survival are greatly improved if emergency care begins within one hour of an accident (such as a car accident) or onset of acute illness (such as a heart attack). This critical time frame is commonly known as the "golden hour."

Some emergency departments in smaller hospitals are located near a helipad which is used by helicopters to transport a patient to a trauma center. This inter-hospital transfer is often done when a patient requires advanced medical care unavailable at the local facility. In such cases the emergency department can only stabilize the patient for transport.

Some patients arrive at an emergency department for a complaint of mental illness. In many jurisdictions (including many U.S. states), patients who appear to be mentally ill and to present a danger to themselves or others may be brought against their will to an emergency department by law enforcement officers for psychiatric examination. From the emergency department, patients thought to be mentally ill may be transferred to a psychiatric unit (in many cases involuntarily).

An ED requires different equipment and different approaches than most other hospital divisions. Patients frequently arrive with unstable conditions, and so must be treated quickly. They may be unconscious, and information such as their medical history, allergies, and blood type may be unavailable. ED staff are trained to work quickly and effectively even with minimal information.

ED staff must also interact efficiently with pre-hospital care providers such as EMTs, paramedics, and others who are occasionally based in an ED. The pre-hospital providers may use equipment unfamiliar to the average physician, but ED physicians must be expert in using (and safely removing) specialized equipment, since devices such as Military Anti-Shock Trousers ("MAST") and traction splints require special procedures. Among other reasons, given that they must be able to handle specialized equipment, physicians can now specialize in emergency medicine, and EDs employ many such specialists.

ED staff have much in common with ambulance and fire crews, combat medics, search and rescue teams, and disaster response teams. Often, joint training and practice drills are organized to improve the coordination of this complex response system. Busy EDs exchange a great deal of equipment with ambulance crews, and both must provide for replacing, returning, or reimbursing for costly items.

Cardiac arrest and major trauma are relatively common in EDs, so defibrillators, automatic ventilation and CPR machines, and bleeding control dressings are used heavily. Survival in such cases is greatly enhanced by shortening the wait for key interventions, and in recent years some of this specialized equipment has spread to pre-hospital settings. The best-known example is defibrillators, which spread first to ambulances, then in an automatic version to police cars, and most recently to public spaces such as airports, office buildings, hotels, and even shopping malls.

Because time is such an essential factor in emergency treatment, EDs typically have their own diagnostic equipment to avoid waiting for equipment installed elsewhere in the hospital. Nearly all have an X-ray room, and many now have full radiology facilities including CT scanners and ultrasonography equipment. Laboratory services may be handled on a priority basis by the hospital lab, or the ED may have its own "STAT Lab" for basic labs (blood counts, blood typing, toxicology screens, etc) that must be returned very rapidly.

Emergency departments around the world are increasingly being used for non-emergency care because of overburdened healthcare systems. Many people, afflicted by minor injuries or illnesses late at night or at times when their doctor's office is closed, are forced to resort to attending the ED. This is especially true for conditions with distressing symptoms, such as a child's ear infection. People in lower socioeconomic classes are more likely to use the ED for primary care services, as they typically find it inconvenient or impossible to miss work for a doctor's office visit.

In the United Kingdom, it has become more popular to visit the A&E since it became mandatory for patients to be fully treated and discharged from the department within four hours of arrival. Also, the introduction of the new contract for primary care physicians in that country decreased the accessibility of general practitioner (GP) services. Under this contract GPs can opt out of on-call cover, and patients sometimes present instead to the A&E.